Numerous prior art arrangements are known for the filtration of dirty gas by passing the dirty gas through a bed of granular material, for example gravel.
In many applications, a fixed bed of gravel is used where the gas flows through the bed and particulate materials removed from the gas stream build up within the bed. Ultimately, the flow of gas in the cleaning direction is terminated and gas flow is reversed to remove the accumulated particulate material from the filter bed. Subsequently a new gas cleaning cycle is initiated.
Some other prior art arrangements provide means for utilization of a moving gravel bed filter where new media is continuously or intermittently added to the filter bed while a substantially equal portion of, presumably dirty, media which has accumulated substantial quantities of the particulate matter to be removed from the gas stream, is removed from the bed.
One such arrangment is shown in U.S. Pat. No. 3,716,969 Maeda where a bed of particulate matter flows downwardly through a filtering section while the gas stream is passed transversely through the media relative to the direction of the flow of media. Thomason, U.S. Pat. No. 1,570,869 shows a similar arrangement where a dirty gas is cleaned by passing the gas transversely through a downwardly moving bed of particulate media.
It is well known in the art, that in filtration of particulate materials from a gas stream the particulate material accumulates in the media to reduce the size of the openings between media granules and the most efficient cleaning occurs in such portions of the media bed where substantial quantities of particulate matter have acumulated inasmuch as the flow area provided by the interstices between the particulate filter material is reduced so small particles which pass through clean media are retained to improve the overall efficiency of removal of particulate material from the gas stream.
In general, known prior art moving bed arangements where gas flows transverse to the direction of media flow are less effective than arrangements where gas flows through the length of the bed, as provided by the present invention because in arrangements where the gas flows transversely through the media as the media flows through the filtration area, and particulate matter accumulates on the media to restrict flow of gas through the dirty areas of the media, gas flow is simply diverted to the cleaner portions of the moving media where removal efficiency is lower.
Therefore, in prior art arrangements where accumulation of particulate material on the moving media simply increases pressure drop through the portion of the media where the particulate matter has accumulated, and diverts gas flow to other, cleaner, areas of the media, the inherent advantage of the efficient cleaning which would occur in the dirtier portions of the media is lost.